1. Field of the Invention
The present invention relates to a lens-interchangeable video camera apparatus.
2. Related Background Art
Interchangeable lenses have been conventionally used in the field of cameras, and appropriate lenses can be selected in accordance with photographic conditions and applications.
As another tendency, various functions such as focus control, exposure control, and zoom control, all of which are required to operate a camera, are automated to improve operability. These automatic functions must be equipped as standard functions.
The recent developments in video equipment such as a video camera and an electronic still camera have been remarkable. Interchangeable lenses which have been conventionally used in only sliver-chloride film cameras except for some special equipment are proposed to be used in video cameras.
Optimal lens units can be selected in accordance with photographic conditions and applications, and the range of use of video cameras can be remarkably increased.
When interchangeable lenses are to be used in video cameras, video camera interchangeable lenses must be newly designed. However, demand may have arisen for use/connect interchangeable lenses for silver chloride film cameras in video cameras. It is therefore expected that an adapter for connecting any lens unit to a video camera be necessary.
In an interchangeable lens type camera unit of this type, a control signal is sent from a camera side to a lens unit side to control each drive system in the lens unit. For example, no problem occurs when a still camera lens unit is mounted on the camera body to perform a manual operation. However, when automatic control is to be performed from the camera side, a system cannot perform a normal auto focus operation even if the system mounted with the still camera lens unit is to be controlled as in a system mounted with a video interchangeable lens system due to the following reasons. A focus encoder may not be arranged. Even if it is arranged, the encoder area divisions are not equal to those of the video lens unit. A focus ring cannot be stopped at an optimal position even if the focus ring is controlled to be stopped at a boundary of divisions of the encoder.
When interchangeable lenses are to be mounted on video cameras and a lens unit (e.g., an existing still camera lens unit) having standards different from those of a video camera lens unit is to be connected to a video camera, an adapter is required to connect a lens unit for a silver chloride film camera to a video camera because mounts for the still and video cameras are different from each other and various differences caused by still image photography and moving image photography are present in operation and control systems.
In connection of an existing still camera lens unit to a video camera through an adapter, since design and specifications of the video camera lens are different from those of the still camera lens unit, data cannot be directly exchanged between the video camera and the mounted lens unit. For example, in an auto focus operation, an appropriate auto focus speed cannot be selected.
More specifically, a stable auto focus operation cannot be performed in lenses having different image variable magnification factors corresponding to a movement of a distance ring unless a control speed is set variable.
For example, at a nearly focused position, hunting occurs to largely change an image angle in a lens having a large image variable magnification factor as in a video camera lens unless a focus speed is controlled to be reduced. On the other hand, in a lens having a small image variable magnification factor as in a still camera lens, a change in image angle is small even if hunting occurs because the focus speed is controlled to be relatively high. However, if the focus speed is controlled as in the video camera lens, the focus speed is too low in the still camera lens although it is appropriate for the video camera lens.
Since the shortest range photographic distances of the video camera lens unit and the still camera lens unit are different from each other, a period required for shifting the state from a much unfocused state to a nearly focused state in the video camera lens unit is largely different from that in the still camera lens.
Appropriate control cannot be performed when a still camera lens unit is simply connected to a video camera unit.